Composite disc brake backing plate

ABSTRACT

A brake backing plate includes first and second sheet metal stampings. Each sheet metal stamping has a respective textured face with a plurality of integrally formed piercing members. A solid non-porous metal core is sandwiched between the first sheet metal stamping and the second sheet metal stamping. The piercing members of the first sheet metal stamping penetrate into the metal core, and the piercing members of the second sheet metal stamping penetrate into the metal core, to secure the first sheet metal stamping, the second sheet metal stamping, and the metal core together.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/534,653, filed on Nov. 6, 2014 and issued as U.S. Pat. No.9,273,741 on Feb. 10, 2016, which claims priority from Canadian patentapplication No. 2,865,384, filed on Sep. 26, 2014, the contents of bothof which are incorporated herein by reference in their entirety.

FIELD

The specification relates to disc brake pads, and more specifically tometallic backing plates of disc brake pads, to which wearable frictionmaterial can be attached.

BACKGROUND

U.S. Pat. No. 5,376,410 (MacKelvie) purports to disclose a method fortreating a surface which is to be bonded to another surface. The methodcomprises displacing a portion of the surface material to a positionsuch that the displaced material, while remaining an integral part ofthe surface, forms a burr which is adapted to mechanically engage aflexible material placed adjacent thereto to thereby provide amechanical interlocking action.

European Patent Application Publication No. EP0859163A1 (Sundheim)purports to disclose a pad holder that is a structure made of aheat-resistant foamed material, especially aluminum foam, with a sheetof high strength metallic material, especially a steel sheet. Thestructure may be a sandwich-like composite consisting of a structurallayer of the foamed material, which at least on one side is bonded witha steel sheet.

SUMMARY

The following summary is intended to introduce the reader to variousaspects of the applicant's teaching, but not to define any invention

Disclosed herein is a composite disc brake backing plate (also referredto as a brake backing plate or a backing plate) that may be made fromfirst and second sheet metal stampings and a metal core. The metal coremay be relatively soft (i.e. softer than the first and second sheetmetal stampings). Each sheet metal stamping may have a respectivetextured face with a plurality of integrally formed piercing members.Each piercing member may have a distal end. The metal core may besandwiched or laminated between the first sheet metal stamping and thesecond sheet metal stamping. The metal core may be sufficiently soft andthe sheet metal may be sufficiently hard so that under pressure, thepiercing members of the sheet metal are able to pierce (or penetrate)into the metal core. The textured face of the first sheet metal stampingcan be rolled or pressed into the first face of the metal core so thatthe piercing members pierce into the metal core. The textured face ofthe second sheet metal stamping can be rolled or pressed into the secondface of the metal core so that the piercing members pierce into themetal core. This can secure the first sheet metal stamping, the secondsheet metal stamping and the metal core together.

The metal core can be solid and non-porous (e.g. a solid non-porous slabof aluminum). The use of a solid non porous metal core provides asubstrate into which the piercing members can solidly embed, andstrongly mechanically engage. In other words, all or the majority of thepiercing members engage the metal core, and they engage the metal corealong their entire outer surface or the majority of their outer surface.This allows for a tight locking-taper fit between the piercing membersand the metal core, and provides for a bond between the sheet metalstampings and the metal core that is sufficient to withstand forcesexperienced by the brake backing plate during braking.

This is in contrast to porous materials, which would not provide asubstrate into which piercing members can solidly embed and stronglymechanically engage. That is, if the metal core were porous, themajority of the piercing members would not necessarily engage the metalcore, and the piercing members would not necessarily engage the metalcore along the majority of their outer surface. Any bond provided by thepiercing members between a porous material and the sheet metal stampingsis therefore expected to be insufficient to withstand forces experiencedby the backing plate during braking.

Furthermore, certain porous materials are highly compressible orcrushable. For example, aluminum foams (such as that described bySundheim) are prone to failure by crushing. Such porous materials arenot expected to withstand the forces imparted by the rolling or pressingof the piercing members into the metal core.

Accordingly, backing plates as described herein may in some examples berelatively lightweight (e.g. as compared to standard steel backingplates), while remaining able to withstand the forces experienced duringbraking, and while retaining the ability to be assembled by rolling orpressing.

In some examples, no bonding material such as adhesive is used informing the brake backing plate. In other examples, adhesive or otherbonding material may be used.

In some examples, each piercing member on each respective sheet metalstamping may extend substantially perpendicularly from the sheet metalstamping and may be tapered so the piercing member has a thickness thatdecreases from the face of the metal stamping to the distal end of thepiercing member. As a result, the metal core may be bound to the firstand second sheet metal stampings by a locking taper fit of the piercingmembers and the metal core.

In some examples, one or both of the first sheet metal stamping and thesecond sheet metal stamping may be made from steel. The metal core maybe made from solid non-porous aluminum (which would exclude aluminumfoams), which may have a hardness of no more than 70 HB. The first andsecond sheet steel stampings may have a hardness of at least 90 HB. Insome examples, the aluminum used to form the core may have a hardness ofno more than 60 HB and the sheet steel first and second steel stampingsmay have a hardness of at least 100 HB.

In some examples, the first sheet metal stamping and the second sheetmetal stamping may have a thickness of at least 0.8 mm, and the metalcore may have a thickness of at least 2.5 mm.

In some examples, the first sheet metal stamping may have a secondtextured face with a plurality of integrally formed retention barbsextending from the face for attaching to a friction material to form abrake pad.

The piercing members may be formed without piercing through orperforating the sheet metal stampings.

The specification further provides methods of making brake backingplates from first and second sheet metal stampings and a metal core.Each sheet metal stamping may have the same profile and each may have arespective textured face with plurality of integrally formed piercingmembers. Each piercing member may extend from the face of one of thesheet metal stampings to a distal end. The metal core may have the sameprofile as the sheet metal stampings and may have two faces (i.e. afirst face and a second face). The first metal stamping may be pressedor rolled onto the first face of the metal core causing the piercingmembers on the textured face of the first sheet metal stamping to piercethe first face of the metal core, thereby locking the first sheet metalstamping and the metal core together. Similarly the second sheet metalstamping may be pressed or rolled onto the second face of the metal corecausing the piercing members on the textured face of the second sheetmetal stamping to pierce the second face of the metal core, therebylocking the second sheet metal stamping and the metal core together.

According to some aspects, a brake backing plate comprises first andsecond sheet metal stampings. Each sheet metal stamping has a respectivetextured face with a plurality of integrally formed piercing members.The brake backing plate further comprises a solid non-porous metal core.The metal core is sandwiched between the first sheet metal stamping andthe second sheet metal stamping. The piercing members of the first sheetmetal stamping penetrate into the metal core, and the piercing membersof the second sheet metal stamping penetrate into the metal core, tosecure the first sheet metal stamping, the second sheet metal stamping,and the metal core together.

The metal core may be softer than the first and second sheet metalstampings.

At least one of the first sheet metal stamping and the second sheetmetal stamping may be steel.

The metal core may comprise aluminum. The metal core may be a solidnon-porous aluminum slab.

The first sheet metal stamping and the second sheet metal stamping mayeach have a thickness of at least 0.8 mm, and the metal core may have athickness of at least 2.5 mm.

The first sheet metal stamping or the second sheet metal stamping mayinclude a second textured face with a plurality of integrally formedretention barbs for attaching to a friction material to form a brakepad.

The first and second sheet metal stampings may be non-perforated.

According to some aspects, a method of manufacturing a brake backingplate comprises the steps of: a) positioning a first sheet metalstamping adjacent a first face of a solid non-porous metal core; b)positioning a second sheet metal stamping adjacent an opposed secondface of the solid non-porous metal core; c) applying pressure to thefirst sheet metal stamping to force a plurality of integrally formedpiercing members of the first sheet metal stamping to pierce the metalcore to secure the first sheet metal stamping to the metal core; and d)applying pressure to the second sheet metal stamping to force aplurality of integrally formed piercing members of the second sheetmetal stamping to pierce the metal core to secure the second sheet metalstamping to the metal core.

Steps c) and d) may be carried out simultaneously. Steps c) and d) maycomprise at least one of rolling and pressing the first sheet metalstamping, the metal core, and the second sheet metal stamping.

The method may be carried out without applying a bonding materialbetween the sheet metal stampings and the metal core.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings included herewith are for illustrating various examples ofarticles, methods, and apparatuses of the present specification and arenot intended to limit the scope of what is taught in any way. In thedrawings:

FIG. 1 is a cross-sectional view through one row of piercing members onan example sheet metal stamping, also showing a shallow groove that thetexturizing tooling can cut to raise each piercing member;

FIG. 1a is an end view of the sheet metal stamping of FIG. 1, showingeight rows of piercing members;

FIG. 2 is a cross-sectional view of another example sheet metalstamping, which is textured on both faces, where the cross section istaken through one row of piercing members on the lower face and one rowof hooked retention barbs on the upper face;

FIG. 3 is a top view of an example disc brake backing plate includingthe sheet metal stamping of FIG. 1 and the sheet metal stamping of FIG.2, which provides the rotor-facing face of the backing plate with hookedretention barbs; and

FIG. 4 is a partial cross-sectional view of the backing plate of FIG. 3taken along line 4-4 in FIG. 3.

DETAILED DESCRIPTION

Various apparatuses or processes will be described below to provide anexample of an embodiment of the claimed subject matter. No embodimentdescribed below limits any claim and any claim may cover processes orapparatuses that differ from those described below. The claims are notlimited to apparatuses or processes having all of the features of anyone apparatus or process described below or to features common tomultiple or all of the apparatuses described below. It is possible thatan apparatus or process described below is not an embodiment of anyexclusive right granted by issuance of this patent application. Anysubject matter described below and for which an exclusive right is notgranted by issuance of this patent application may be the subject matterof another protective instrument, for example, a continuing patentapplication, and the applicants, inventors or owners do not intend toabandon, disclaim or dedicate to the public any such subject matter byits disclosure in this document.

Disclosed herein is a composite disc brake backing plate. In someexamples, to make the plate, a metal core, which may be relatively softand lightweight, is sandwiched or laminated between first and secondsheet metal stampings, which may be harder than the metal core. The corematerial may be a solid and non-porous, such as a solid and non-porousaluminum slab. The first and second sheet metal stampings may be steel.The sheet metal stampings and the metal core may each have substantiallythe same profile (where the profile is the shape and dimensions seen ina plan view like that shown in FIG. 3) so that the sheet metal stampingsand the metal core can be aligned to form a disc brake backing platehaving that same profile. The thicknesses of the three portions (in thedirection going into the page in FIG. 3) are discussed below.

A respective face of each of the first and second sheet metal stampingsmay be texturized with a plurality of integral piercing members. In someexamples, the piercing members may be relatively straight, extendinggenerally perpendicularly from the face of the sheet metal stamping to adistal end spaced from the face. The piercing members may be tapered andstocky so that the tips and shank of each piercing member have thestrength to pierce the metal core without deforming by bending, hooking,or blunting. Such tapered piercing members may have a pointed profile.The respective other (or second) face of one or both sheet metalstampings may be texturized with retention barbs having a curved/hookedprofile for retention of flowable material, and in a variety of sizesand densities. Barb-textured metal is available from Nucap IndustriesInc. of Toronto Ontario, Canada.

On the respective face of each sheet metal stamping that is adjacent themetal core, the piercing members may be tapered and pointed, so that byapplying pressure to the first sheet metal stamping, the metal core, andthe second sheet metal stamping, such as by rolling or pressing, thepiercing members pierce into respective opposite faces (i.e. first andsecond faces) of the metal core, thereby securing the three layerstogether into a solid backing plate, optionally without the use ofbonding material such as adhesive. The tapering of the piercing memberscan result in a strong locking taper fit between the layers.

As mentioned above, the metal core can be solid and non-porous, such asa solid non-porous aluminum slab. The use of a solid non-porous materialprovides a substrate into which the piercing members can solidly embed,and strongly mechanically engage. In other words, all or the majority ofthe piercing members engage the metal core, and they engage the metalcore along their entire outer surface or the majority of their outersurface. This allows for a tight locking-taper fit between the piercingmembers and the metal core, and provides for a bond between the sheetmetal stampings and the metal core that is sufficient to withstandforces experienced by the backing plate during braking.

As used herein, the term “solid and non-porous” with respect to themetal core excludes foamed materials, such as aluminum foams, which areporous.

The locking taper fit of each piercing member in a solid non-porousmetal core material as the two are driven together can result in highfrictional forces and corresponding resistance to withdrawal of thepiercing members. This locks or secures the materials together.

One or both of the sheet metal stampings may also have a second facetextured with a plurality of integrally raised retention barbs forattaching suitable materials. On the upper face of the first stampingthere may be retention barbs over which brake friction material ismoulded.

In the examples shown herein, both piercing members and retention barbsare formed on the surfaces without piercing or perforating through thesheet metal stampings.

The sheet metal stampings may have the required shape and dimensions fora finished brake backing plate prior to assembly, or may be trimmedafter assembly.

Referring now to FIGS. 1 and 1 a, a sheet metal stamping 100 is shown.Piercing members 102 extend from sheet metal stamping 100 on a firstface 104 thereof.

An alternative sheet metal stamping 200 is shown in FIG. 2. In thisexample, the first sheet metal stamping 200 includes piercing members202 on a first face 204 thereof, and also retention barbs 208 thatextend from the first sheet metal stamping 200 on a second face 210thereof. Piercing members 202 and retention barbs 208 are on oppositefaces of the same stamping. The sheet metal stamping 200 may be used asthe friction-receiving side of a disc brake backing plate (e.g. backingplate 414 shown in FIG. 4).

In the example shown, the piercing members 102, 202 are tapered, stocky,relatively straight and substantially perpendicular to the face fromwhich they extend. The texturizing tooling (now shown) that raises thepiercing members 102, 202 plows rows of stop-grooves with toothedblades, and so the piercing members 102, 202 in the example shown are inparallel rows. FIG. 1 shows the piercing member-to-piercing memberspacing within a row of piercing members 102, and FIG. 1 a shows the rowspacing.

Referring to FIGS. 3 and 4, an example disc brake backing plate 414 isshown. The disc brake backing plate 414 includes a first sheet metalstamping 400 a, a second sheet metal stamping 400 b, and a metal core416. In the example shown, the first sheet metal stamping 400 a is inaccordance with the sheet metal stamping 100 of FIG. 1 (i.e. haspiercing members 402 a on its first face 404 a only), and the secondsheet metal stamping 400 b is in accordance with the sheet metalstamping 200 of FIG. 2 (i.e. has piercing members 402 b on its firstface 404 b and retention barbs 408 on its second face 410 b).

FIG. 3 is a top view of the rotor-facing side of the disc brake backingplate 414, which includes holes B, into which friction material may flowand harden to solidify and help retain friction material on the surfaceof the plate.

Referring to FIG. 4, the metal core 416 in the example shown is arelatively soft and lightweight metal, and is solid and non-porous. Thepiercing members 402 a of the first face 404 a of the first sheet metalstamping 400 a pierce and penetrate the metal core 416. The piercingmembers 402 b of the first face 404 b of the second sheet metal stamping400 b pierce and penetrate the metal core 416. The hooked retentionbarbs 408 on the second face 410 b of the second sheet metal stamping400 b face away from the metal core 416.

In alternative examples, a backing plate can be provided withoutretention barbs. The friction material may be bonded and/or riveted to aplain face surface.

The composite disc brake backing plate 414 described herein may be anextremely stiff, rigid laminate. This is believed to be because, when amaterial with piercing members is bent, for example into a convex orarched shape, the free-standing tips of the raised piercing memberswould naturally have to spread apart or fan-out across the curve.However when piercing members are embedded in a substrate such as ametal core, the tips are also locked or fixed therein and prevented fromspreading. The result is a situation where each piercing membercontributes to the overall stiffness of the composite plate. In thisway, a stiff laminate is created from what would otherwise be relativelyflexible sheets of metal (due to their relative thinness).

Various types, qualities and grades of metals may be used for thestampings and the core (e.g. stainless steel, regular steel, aluminum),including cheaper or lower grade metals that might not ordinarily beconsidered for backing plate use.

In some examples, adhesive or other bonding material may not be employedto bond the sheet metal stampings 400 a, 400 b to the metal core 416. Insuch examples, the bond between the sheet metal stampings 400 a, 400 b,and the metal core 416 may rely on the ability of the piecing members402 a, 402 b on the first faces 404 a, 404 b of the sheet metalstampings 400 a, 400 b to pierce and penetrate the metal core 416 andcreate a locking taper fit. It has been found that tapered piercingmembers 402 raised on steel stampings can penetrate an aluminum core andthereby secure the steel and aluminum tightly together.

To form the composite disc brake backing plate 414, a slab of metal forthe metal core 416, such as a relatively soft, lightweight, solid, andnon-porous aluminum slab may be sandwiched between the first sheet metalstamping 400 a (e.g. a sheet steel stamping), and the second sheet metalstamping 400 b(e.g. a sheet steel stamping). For example, the firstsheet metal stamping 400 a may be positioned adjacent a first face 418of the metal core 416, and the second sheet metal stamping 400 b may bepositioned adjacent an opposed second face 420 of the metal core 416.

Pressure may then be applied to the first sheet metal stamping 400 a toforce the piercing members 402 a thereof to pierce the metal core 416 tosecure the first sheet metal stamping 400 a to the metal core 416, andto the second sheet metal stamping 400 b to force the piercing members402 b thereof to pierce the metal core 416 to secure the second sheetmetal stamping 400 b to the metal core 416. The first and second 400 bsheet metal stampings may be secured to the metal core 416 in a singlestep (i.e. simultaneously), or in separate steps. The pressure may beapplied for example by a roller or a press.

The use of a solid and non-porous metal core 416 may allow for theapplication of pressure to force the piercing members 402 a to piercethe metal core 416, without crushing or compressing the metal core 416.That is, certain porous materials such as metal foams are prone tofailure by crushing. Such porous materials are not expected to withstandthe forces imparted by the rolling or pressing of the piercing membersinto the metal core.

In some examples, the metal core 416 may be about 3.2-4.8 mm(0.125-0.1875 inches) thick and may be aluminum with an H32 temper(strain-hardened and stabilized, quarter-hard) and a Brinell hardness ofabout 60 HB. This may be formed from a standard 5052-H32 aluminum sheetfor example. The sheet metal stampings 400 a, 400 b may be, for example,1010-full hard or J1392 steel, with a Brinell hardness of about 105 HB.The thickness of the rotor/caliper-facing sheet metal stamping 400 b towhich friction material is attached may in some examples be about1.0-1.5 mm (0.04-0.06 inches) thick, and the thickness of thepiston-facing steel metal stamping 400 a may in some examples be about1.5-1.9 mm (0.06-0.07 inches). For both sheet metal stampings 400 a, 400b, the piercing members 102 may have a density of about 7-8 piercingmembers per square centimetre (about 48 per square inch), with a heightof about 1.5-1.8 mm (0.06-0.07 inches).

The following example shows a weight comparison of a composite discbrake backing plate 414 as described herein, versus a standard steeldisc brake backing plate. The composite disc brake backing plate 414 isabout 32% lighter than a standard solid steel disc brake backing platefor the same vehicle part number.

Overall Steel Core thickness thickness thickness Overall weight Standardsteel 0.220 inch 0.220 inch N/A 0.417 lb backing plate (5.6 mm) (5.6 mm)(0.917 kg) Composite 0.220 inch 0.040 inch 0.125 inch 0.284 lb backingplate (5.6 mm) (1 mm); (3.17 mm) (0.625 kg) 0.060 inch (1.5 mm)

As a strength comparison, the following table shows the results of adeflection test of an instance of a composite aluminum and steellaminated material as described above (e.g. as shown in FIG. 4) comparedto the same size bar of soft aluminum. The loads were progressivelyincreased from Load 1 to Load 3 and demonstrate a remarkably lowerdeflection of the composite bar compared to the aluminum bar. In thecase of Load 3, the aluminum bar bent/deflected beyond the test set-uptravel limit of about 10 mm (0.400″).

Load 1 Load 2 Load 3 Test piece Deflection Deflection DeflectionComposite 0.013 inch 0.040 inch 0.100 inch bar (0.33 mm) (1 mm) (2.5 mm)Aluminum 0.025 inch 0.120 inch Elastic limit bar (0.6 mm) (3 mm)exceeded

The layers of the composite disc brake backing plate 414 may be rolledor pressed to achieve embedding (e.g. full embedding) of the piercingmembers 402 of the sheet metal stampings 400 in the metal core 416. Insome examples, every piercing member 402 on the respective first faces404 a, 404 b of each of the stampings 400 a, 400 b pierces and extendsinto the metal core 416. Application of heat may also be useful ornecessary in certain circumstances. Where a sheet metal stamping withboth faces textured is used (e.g. sheet metal stamping 400 b in FIG. 4),the rolling or pressing may be done using methods to avoid breaking orcrushing the piercing members on the outer surfaces of the stampings,such as by using a grooved roller to follow tracks between rows ofpiercing members, or, a press plate having a knurled surface.

In some examples, each piercing member 402 may have a thickness of about0.8 mm to 1.3 mm for steel with a Brinell hardness of at least 90 BH,and optionally 100-110 BH or greater. The density of the piercingmembers may be about 4.7 to 11.6 per square cm (30-75 per square inch),although may also be higher or lower in some examples.

The tapering of the piercing members 402 may be smooth to facilitatepenetration of the metal core 416 so that the thickness of the piercingmembers 402 near the top of each piercing member 402 is substantiallyless than the thickness at the base, where the piercing member extendsfrom the face of the sheet metal stamping 400 a, 400 b. For example, thethickness of the piercing members 402 proximate to their tips may be 50%or less of the thickness of the piercing members 402 at their base.

Additionally, although the composite disc brake backing plate 414 shownand described above has two sheet metal stampings 400 a, 400 b,multi-layer composite disc brake backing plates are also possible, byhaving more than one core layer and the corresponding number of sheetmetal stampings (not shown). For example, a five-layer backing platecould have two outer sheet metal stampings, each having piercing memberson their inner face, and an inner stamping having piercing members onboth faces, with two metal core layers, each metal core layer beingbetween the inner sheet metal stamping and the textured face of one ofthe outer sheet metal stampings.

The abbreviation mm as used herein refers to millimeters. Theabbreviation cm as used herein refers to centimeters.

While the above description relates to laminates in the form of diskdisc brake backing plates, the laminates described herein may have otheruses. Such uses may include but are not limited to structural panels,tooling, and dies and presses.

The invention claimed is:
 1. A brake backing plate comprising: a) firstand second sheet metal stampings, each sheet metal stamping having arespective textured face with a plurality of integrally formed piercingmembers; and b) a solid non-porous metal core, the metal core sandwichedbetween the first sheet metal stamping and the second sheet metalstamping, the piercing members of the first sheet metal stampingpenetrating into the metal core, and the piercing members of the secondsheet metal stamping penetrating into the metal core, to secure thefirst sheet metal stamping, the second sheet metal stamping, and themetal core together.
 2. The brake backing plate of claim 1, wherein themetal core is softer than the first and second sheet metal stampings. 3.The brake backing plate of claim 2, wherein the metal core comprisesaluminum.
 4. The brake backing plate of claim 1, wherein at least one ofthe first sheet metal stamping and the second sheet metal stamping issteel.
 5. The brake packing plate of claim 4, wherein the metal core isa solid non-porous aluminum slab.
 6. The brake backing plate of claim 1,wherein the first sheet metal stamping and the second sheet metalstamping each have a thickness of at least 0.8 mm, and the metal corehas a thickness of at least 2.5 mm.
 7. The brake backing plate of claim1, wherein one of the first sheet metal stamping and the second sheetmetal stamping includes a second textured face with a plurality ofintegrally formed retention barbs for attaching to a friction materialto form a brake pad.
 8. The brake backing plate of claim 1, wherein thefirst and second sheet metal stampings are non-perforated.
 9. A methodof manufacturing a brake backing plate, the method comprising the stepsof: a) positioning a first sheet metal stamping adjacent a first face ofa solid non-porous metal core; b) positioning a second sheet metalstamping adjacent an opposed second face of the solid non-porous metalcore; c) applying pressure to the first sheet metal stamping to force aplurality of integrally formed piercing members of the first sheet metalstamping to pierce the metal core to secure the first sheet metalstamping to the metal core; and d) applying pressure to the second sheetmetal stamping to force a plurality of integrally formed piercingmembers of the second sheet metal stamping to pierce the metal core tosecure the second sheet metal stamping to the metal core.
 10. The methodof claim 9, wherein steps c) and d) are carried out simultaneously. 11.The method of claim 9, wherein steps c) and d) comprise at least one ofrolling and pressing the first sheet metal stamping, the metal core, andthe second sheet metal stamping.
 12. The method of claim 9, wherein themethod is carried out without applying a bonding material between thesheet metal stampings and the metal core.